Explicite iteration

explicite-iteration.clj

(require '[clojure.java.io :as io])

(def in-file "/path/to/datafile-4gb.tsv")
(def out-file "/path/to/datafile-16gb.tsv")

(defn multiply-string [s n]
  (cond
   (> n 1) (str s \newline (multiply-string s (dec n)))
   (= n 1) (str s \newline)
   :else nil))

(defn multiply-file [in out n]
  (with-open [reader (io/reader  in)
              writer (io/writer out)]
    (loop [line (.readLine reader)]
      (if (nil? line)
          nil
          (do
            (.write writer (multiply-string line n))
            (recur (.readLine reader)))))))


user> (time (multiply-file in-file out-file 4))
"Elapsed time: 612539.345864 msecs"
nil
user> (/ 612539.345864 812899000)
7.535245410118601E-4

user> (def in-file "/path/to/datafile-16gb.tsv")
#'user/in-file
user> (def out-file "/path/to/datafile-64gb.tsv")
#'user/out-file
user> (time (multiply-file in-file out-file 4))

"Elapsed time: 2476705.02482 msecs"
nil
user>
user> (/ 2476705.02482 (* 812990000 4))
7.616037788964194E-4